The present invention relates to a light polarizing ophthalmic lens made of organic glass with an optically transparent composite film exhibiting both impact-resistance and polarizing properties, and to a process for its manufacture.
It is known that the manufacture of polarizing lenses raises various problems related to the solubility of the polarizing materials (generally polarizing particles) in the surrounding environments, as well as their very low mechanical strength.
A number of solutions have been proposed in the state of the art.
Some of them have consisted in associating an organic polarizing film of the polyvinyl alcohol type with one or two (“sandwich”) elements of glass. These solutions of the prior art have the following disadvantages:                the complexity of bonding the polarizing film to an optical substrate without deforming the direction of polarization, as indicated in the French patent FR 76 18891,        the weight of the assemblies thus obtained, which are not compatible with conventional lenses utilised in spectacles, and finally,        the extremely high cost of such products, which is a result of their complexity.        
Other solutions have consisted in providing polarizing films of the polyvinyl acetate or polyvinyl butyrate type bonded onto the concave face of an inorganic spectacle lens. But these films have a very poor optical quality and a significant sensitivity to scratching. Furthermore, it is necessary to protect them from moisture.
U.S. Pat. No. 4,977,028, U.S. Pat. No. 4,865,668, U.S. Pat. No. 4,683,153 and U.S. Pat. No. 4,648,925 describe laminated, transparent, polarizing glass articles, comprising a support of inorganic or organic glass having parallel microgrooves, formed on one of the faces of the support, a polarizing coating deposited on the said face of the support, and a composite film of polyurethane constituted by a thermoplastic polyurethane side and a thermosetting polyurethane side, the thermoplastic polyurethane side adhering to the polarizing coating. However, a consequence of this technique is that it is necessary to replace the whole lens if defects appear in the microgrooves. Another consequence of this technique is that the impact strength is reduced at the microgrooves. Furthermore, nothing is said concerning the mechanical strength of the lens.
Japanese patent application H2-96371 describes a method for forming a polarizing film having a polarizing function, which is applied to liquid crystal display components (LCD). The polarizing film is a layer of photosensitive resin dyed using iodine or a dichromatic dye as the polarizing element. Numerous fine grooves are formed in the surface of this layer of photosensitive resin by performing interference exposure and development processes using holographic techniques. The polarizing element is oriented and dyed in these fine grooves. However, nothing is said in this patent application concerning the mechanical strength of this polarizing film.